This invention relates to the measurement of relatively large currents, namely those in the range of a hundred or so amperes to at least several thousands of amperes, especially in the context of motor controllers for electrically powered vehicles.
Electrically powered vehicles have recently become more important as environmental concerns grow. A problem with electrically powered vehicles is that with current technology, vehicle range is limited to an extent that many users find inconvenient. The use of hybrid internal-combustion/electric vehicles has been proposed in order to address the problem of limited range, and such vehicles are beginning to find use. Another problem with electrically powered or partially electrically powered vehicles is that the technology is not well developed for storing large amounts of electrical energy as may be required, and for controllably converting the energy so stored into usable vehicle traction motor current.
Many electrical power and drive schemes have been proposed and tried. Many of these techniques rely on microprocessor- or digital-signal-processor-controlled controllers, which perform sophisticated analyses for generating the desired control signals which, in turn, control the application of relatively large traction currents to the vehicle traction motor. Among these sophisticated control schemes are the field-oriented-control (FOC) applied to induction traction motors. Sophisticated controllers generally require substantial information about the vehicle operator commands, the state of the battery charge, the vehicle speed, and the motor current or currents, in the context of multiphase or polyphase motors. Such controllers may also provide for dynamic braking, in which vehicle kinetic energy is returned to the traction battery concurrently with braking. The controllers may also control the operation of an internal combustion engine in the case of hybrid electric vehicles.
As mentioned, the technology is not well developed for operation of vehicle motors from traction storage batteries or from the newer ultracapacitors which may be used for electrical energy storage. For example, battery voltages are in direct-voltage (DC) form, and the traction power may be such as to require currents currently in the range of up to one thousand amperes, but which may be larger in the future. Handling currents in the hundreds or thousands of amperes has long been known, but principally in a laboratory setting. In a laboratory, it is easy to handle such large currents by the use of machined bus bars and large cables. Generally, however, the types of devices used in laboratory settings are not directly usable in the context of a vehicle, where light weight, reliability under adverse weather and operating conditions, and low cost are important factors.
A device for determining electrical current according to an aspect of the invention includes a current sensing apparatus. The current sensing apparatus includes a first electrical path through which a current to be sensed passes. The current sensing apparatus is capable of producing a sensed signal in response to the current in the first electrical path, up to a predetermined maximum value of the current in the first electrical path, above which maximum value of current the sensed signal is limited. First and second terminals are coupled to ends of the first electrical path, whereby, or as a result of which, the current sensing apparatus produces the sensed signal in response to current flowing between the first and second terminals, at least up to the predetermined maximum value. The device further includes a second electrical path extending between the first and second terminals. The second electrical path is effectively in electrical parallel with the first electrical path, so that a portion of current flowing between the first and second terminals flows through the second electrical path rather than through the first electrical path. As a result of this division, the unlimited portion of the sensed signal represents a current between the first and second terminals which is greater than the current above which the current sensing apparatus limits. In a particularly advantageous embodiment of the invention, the current sensing apparatus is noncontacting or isolated as between the first current sensing path and that port at which the sensed signal is generated.
According to another aspect of the invention, a vehicle is powered at least in part by an electric motor. The vehicle comprises a rotational vehicle drive device such as a wheel or a cog. A motor is coupled to the rotational vehicle drive device, for driving the vehicle when the motor drives the rotational vehicle drive device. The vehicle also includes a source of electrical energy; in the context of a purely electrically driven vehicle, this might be the traction battery, or in the context of a hybrid electric vehicle, it might include the traction battery, a generator, or both. An electrical power path extends between the source of electrical energy and the motor. The electrical power path including a controllable electrical power control arrangement, for controllably coupling electrical energy between the source of electrical energy and the motor. In an FOC system, the controllable electrical power control arrangement may be a set of power switches operated by a digital controller. In a direct-current system, the power controller might be as simple as a rheostat. A control circuit is coupled to the controllable electrical power control arrangement, for responding to at least operator control signals and motor current signals, for controlling the motor for driving the vehicle under operator control. A current sensing apparatus is located in the electrical power path, for sensing at least one component of motor current. In the context of a simple direct voltage source and motor, the main motor current is sensed, while in the context of FOC control, all the motor currents but one are sensed. The current sensing apparatus has a maximum rated sensed current or maximum motor current component for which a nonlimited sensed signal representative of the motor current component is generated. A resistive shunt parallels the current sensing apparatus, for shunting at least a portion of the motor current component around the current sensing apparatus. In one embodiment of this version, the resistive shunt comprises a multistrand electrically conductive cable. In another embodiment of this version, the resistive shunt comprises a bus bar. In yet another embodiment of this version, the current sensing apparatus includes a printed-circuit board including an electrically conductive path broken at a break location, together with a commercial current sensor coupled across the break in the current path, for generating the sensed signal representative of the motor current component; in this embodiment, the resistive shunt comprises a further electrically conductive portion of the printed-circuit board. In a preferred embodiment of this version, the current sensing apparatus is a noncontacting current sensing apparatus.
According to another aspect of the invention, an arrangement for determining electrical current comprises a current sensing apparatus. The current sensing apparatus including a first electrical path through which a current to be sensed passes. The current sensing apparatus is capable of producing a sensed signal at a sensed signal port in response to the current in the first electrical path, up to a rated maximum value of the current in the first electrical path. In this aspect of the invention, first and second terminals or electrodes are coupled to ends of the first electrical path, whereby the current sensing apparatus produces the sensed signal in response to current flowing between the first and second terminals or electrodes. A second electrical path extends between the first and second terminals, so that the second electrical path is effectively in parallel with the first electrical path. As a result of these arrangements, a portion of the current flowing between the first and second terminals flows through the second electrical path rather than through the first electrical path, whereby the total current flowing between the first and second terminals is greater than the current flowing in the first electrical path, whereby the current sensing apparatus senses less than the total current flowing between the first and second terminals. In a particularly advantageous version of this aspect of the invention, the current sensing apparatus is noncontacting as between the first electrical path and sensed signal port.